Process of rapid drying of lumber



F. W. RUBIN PROCESS OF RPID DRYIIQNG LUMBER Sept; s, 1925 y 13552;,'734

Filed octs e, .1924

OPEN

/CLOSEU A TTORNE Y5,

Patented Sept. 8, 1925.

FREDERICK 'W'. RUBIN, OF INDIANAPOLIS, INDIANA.

raocass oF RAPID-Danno or Limena.

Application led October 6, 1924. Serial No. 742,067.

To all whom 'it may concern:

Be it known that I,vv FREDERICK W. RUBIN, a citizen of the United States, and a resident of Indianapolis, county of Marion, and State of Indiana, have invented a certain new and useful Process of Rapid Drying of Lumber;l and I do hereby declare that the following is a full, clear, and exact description thereof, reference being had to the accompanying drawings, in which like numerals refer to like parts.l

This invention relates to a forced drying process for lumber and the like.

The chief object of the invention is to'dry lumber or the like in a much shorter time than lheretofore has been the practice and at the same time secure a resultant product that does not have serious objections normally the result of a quick drying process, to-wit, cracks', checks and honey combing.

The chief feature of the process consists in subjecting the lumber to a forced or rapid process and intermittently to a decasing operation which removes the casing produced by a forced drying operation.

Another chief feature of the invention re sides in the process being substantially independent oftemperature'and relative humidity variations normally employed in lumber drying and, therefore, can be automatically controlled to-secure a predetermined cyclic'operation.

Another feature of the invention consists in the removal of the case produced by the exposure to the air of the greenlumber for some little time prior to its .complete` drying in a kiln or compartment :whereby any removed and the lumbeninis substantially for forced or rapid drying.

itially prepared 'lhe full nature of the invention'will be understood from. the accompanying drawings and thel following description and claims:

In the drawings,

matic illustration of one means of4 controlling the steam spray for the dry kilns. Fig.

' 2 is a section taken through a piece of lum- "understood from the ber illustrating diagrammatically the nature of the lumber when first subjected to forced drying. Fig. 3 is the same as Fig. 2, showing the lumber decased. j

The full nature of the invention will be following description and claims: A j The invention consists of `a from said case formation.

Figure 1 is a diagram-- process forl rapidly drying lumber and thelike and is b ased upon the prevention of the' formation of a case thatv would be injurious or objectionable in the linal product.l This case has heretofore been substantially prevented from forming by properly controlling temperature and relative humidity `conditions within the drying compartment or kiln or by manually changing the drying conditions when the operator observed an approaching dangerous degree of checking or case hardenmg.

'The present invention materially reduces the interval necessary for completely drying lumber by subjecting the same to a forced or rapid drying process, the chief feature .of which is the intermittent subjection of the lumber to ydecasing loperations between which it is subjected to a forced drying operation and. these variations-are cyclic and substantially independent of constant manual observation and control, or the relation between temperature and relative humidity.

One form of control for automatically securing intermittent subjection of the lumber to a decasing medium, such as steam, is illustrated ,in Fig. 1 of the accompanying drawings, wherein there is provided a' time switch 10 in the form of a clock having a plurality of minute and hour contact points, the minute contact points being connected 4individually with the minute contact switch the closing solenoid 13, said solenoids being connected with the steam valve 14 for open- I ing or` closing the same. Thus when suitably adjusted by manually setting the contact switches 11 and 12, when the hour hand reaches the contact 3, 6, 9 or 12, for purposes of illustration, the open solenoid will be actuated to open the steam valve and allow steam as a decasing medium to be discharged into the kiln. When the minute hand reaches 15, 'or fifteen minutes later, the switch 11 being set accordingly, the closing solenoid will be energized or closing the valve and shutting 0H the steam, thereby permitting the high temperature of the kiln to rapidly dry the lumber for the next two nhours and forty-five minutes. Such a device is shown and described in the co-pending application Serial N o. 713,601, filed Mayv 15, 1924.

As illustrated in FigsfQ-and 3, the lumber 15 having been submitted to rapid drying without a decasing medium or steam being applied thereto, causes the outer surface to be thoroughly dried so as to become more or less hard and brittle down to a depth represented by the line 16, the interior portion of the lumber still retaining an appreciable amount of moisture indicated at 1'( which cannot escape past the crust or casing thus formed on the exterior. However, the moisture therein becoming highly heated and expanding will force the comparatively brittle crust to crack or check, as indicated at 17.

4 However, if the steam is applied just before the cracking or checking of the exterior takes place, the moisture from the steam will penetrate and soften the crust or case and permit the confined interior moisture to escape while permitting the heat to penetrate to the interior of the lumber and thus dry the same from the inside out.

' Lumberdrying is necessarily variable, de-

pendent upon the cross -section and the nathe cross section the greater the time required for drying, and also the greater the, ydanger' of checking.

As al suggested example of variation for sizes. and materials determined originally by a long series ofl experiments, reference is had to a chart copyrighted in 1924 by Frederick W. Rubin. This chart has been published and is now well circulated in the art. The chart thus identified is not intended to be the last word in rapid lumber drying, but is merely a set of suggested data, whereby good results can be obtained. The intervals and temperatures set forth in the table or chart, therefore, can be modified as desired or determined by subsequent experiment and still be within the scope of this invention. Likewise the chart is not intended to be all inclusive, for only the common North American types and kinds of wood are set-forth. If it be deter- .mined that a checking action depends upon the relation which exists between the cross section of the lumber, the kind of lumber, specific gravity thereof, texture, cellular structure orage, it'may be possible to express algebraically in an equation all ,of these and other known and unknown variable'faotors, whereby the critical drying' temperature or the duration intervals there- -of, as well as the physical characteristics of the decasing medium and the intervals thereof may be determined'.

Briefly, the process consists of the following: Lumber is placed in a kiln, compartment or the like, and preferably subjected to 'a decasing mediumv for a determined period or time interval. The purpose of this treatment, as previously indicated, is to remove the case or case hardening produced by air drying. After subjection to this decasing operation the lumber is permitted to dry at a given temperature which is generally very high so as to force the drying operation. The entire temperature of the wood or lumber is thus raised through its thickness. This forces the m'oisture in the lumber from the heart to the exterior, causing it to gradually work its way outwardly toward the surfaces. In the meantime, however, the surface of the lumber has been drying While the interior has been transferring its moisture to the next outermost portion. Therefore, there is formed in the lumber a `case and this is known as case hardening.

cient to produce a case which is not objec-` tionableor deleterious, the lumber is then subjected to a decasing operation. The decasing operation consists in subjecting the lumber to a decasing medium such as steam orthe like. A convenient, relatively cheap and easily obtained medium that has been found satisfactory is high pressure steamand it has been determined that dry steam is more satisfactory than saturated steam for direct application upon wood or lumber for reducing case hardening conditions. The exact operation is not clearly understood. The following is perhaps as plausible a hypothesis as any that may be advanced to describe the successful operation of the process.

When the lumber is drying at an accelerated rate, that is, forced or rapid drying by applying temperature to the kiln or compartment containing the lumber, the outer exposed surface gives up its moisture and shrinks. This forms a shell or case hardened surface that retards the accelerated moisture discharge from', and the resultant drying of, the wood or lumber. Therefore, the total drying period would be unnecessarily extended if forced drying were continued. In addition thereto continued forced drying would not dry the heart of the lumber, but merely localize on the case and increase the depth and also the dryness thereof and honey comb would result. The application of high pressure stea after the drying period has forced-the drying at a rapid'rate and created a small case,

penetrates the case and reconditions the same, and at the same time penetrates to the heart of the lumber and applies heat thereto as well. After the steam has been Acut oE,-the kiln gradually cools although still at a relatively high temperature and as the temperature falls the heat in the lumber tends to flow toward the outside portion of the lumber carrying with it the moi ture contained within the heart. This heat and moisture transfer continues until a new case is developed which seems to insulate the hea-rt of the vlumber from the drying medium in the kiln. Thereafter the drying is delayed until the decasing operation is repeated. This intermittent decasing permits forced drying in the intervening intervals without producing a resultant fractured or checked lumber. retardation in the drying is dependent primarily upon the fact that the lumber in'its interior is normally at a temperature less than that at the outside of the lumber, and, therefore, the heart of the lumber tends to retain the moisture. Subjection of 'the lumber to high temperature which penetrates the heart thereof drives out the moisture through heat transference 'as previously pointed out.

It is to be understood that the Process is readily adjustable to suitable automatic control means lfor rapidly drying `various kinds of lumber by subjecting the same to intermittent forced drying and intermittent decasing independent of the temperature and relative humidity of the kiln until the desired dryness is attained in the lumber. As previously pointed out this drying period varies for different types of lumber and for different sizes thereof.- Likewise the drying process is variable, that is, the

- duration of the alternate intermittent operations will vary for different types of lum-l ber and may be variedv for the same lumber of different sizes and likewise the duration of each cycle will and may vary.

Since the operation is entirely automatic and independent of allvariable factors except time when once adjusted, several kilns and the like can be simultaneously operated from a relatively low capacity-power plant. This is possible by reason of the certaint of operation and application. of the loa upon the power plant only at predetermined times and only for predetermined periods. By staggering and alternating or successively yconnecting several kilns to the common power plant` and arranging the cycle accordingly not more than one kiln will draw power excessively from plant at any time unless such multiple draft is intentionally desired.

The invention claimed is:

l. A cyclic process for rapidly dryingv The lumber and the like consisting of automatically and alternately subjecting the lumber to a rapid drying operation and to a decasing operation having predetermined periods independently of the relative humidity of the air.

2. A process of rapid lumber drying consisting of automatically and intermittently subjecting fora predetermined period the lumber t'o a decasing medium during the drying operation independently of the relative humidity of the air.

. 3. A process of rapid lumber drying consisting of intermittently subjecting the lumber to a decasing medium during the drying operation independently of temperature and relative humidity variation obtainable duin said drying operation.

cyclic process for rapidly drying lumber and the like, consisting ofl automatically and alternately subjecting lumber to a rapid drying operation and .to a decasing operation independently of the relative humidity of the air.

drying operation and to a decasing operation of predetermined periods independently of the relative humidity of the air.

7. The process of rapidlydrying lumber consisting of automatically and alternately for predetermined periods subjecting the lumber to a case producing drying operation and to a decasing operation before perinanent checking occurs independently 'of the relative humidity of the air.

8. The process of rapidly drying lumber consisting of automatically and alternately foi` predetermined periods subjecting the lumber to temperature sufficiently high to penetrate throughout the same and intermittently subjecting said lumber to a decasing .medium for prevention of a permanently checked case independently of the relative humidity of the air.

9. rlhe process of rapidly drying lumber consisting of automatically subjecting the same to initial decasing treatments, thereafter alternately and successively to a drying operation and a decasing operation of predetermined periods until the desired dryness is obtained independently' of the relative humidity of the air.

In witness whereof, I have hereunto affixed my signature.

l FREDERICK W. RUBIN. 

